Situated primarily in southeastern Venezuela, the Guayanan Highlands ecoregion is distinct from other ecoregions in Amazonia due to its montane physiography. It hosts vast expanses of tall primary rain forest and open, treeless or nearly treeless savannas interrupted by gallery forests.
The Guiana Highlands is a heavily forested plateau and low-mountain region of South America, located north of the Amazon River and south of the Orinoco River. It covers the southern half of Venezuela, all of the Guianas except for the low Atlantic coastal plain, the northern part of Brazil, and a portion of southeastern Colombia.
The region comprises the higher elevations of the Guiana Shield. It is perforated by a series of ancient uplands and highlands between 500 and 3,000 m (1,640 and 9,840 ft) in elevation, the tallest ones are comprised in the Tepui ecoregion.
The Guayanan Highlands Moist Forest Ecoregion is distinct from other ecoregions in Amazonia due to its montane physiography. It hosts vast expanses of tall primary rain forest and open, treeless or nearly treeless savannas interrupted by gallery forests.
Portions of the Guayanan Highlands ecoregion lie in the northernmost tip of Brazil, with small slivers in western Guayana and eastern Colombia. Most of this ecoregion lies within the eastern portion of the Orinoco Basin which drains into the Caribbean Sea from Venezuela. Another portion drains into the Amazon Basin.
The major rivers entering the Orinoco Basin from this ecoregion are the Orinoco headwaters, the Ventuari, Caroní, Paragua, and Caura in Venezuela. In the southern potions, the Rio Uraricuera and Rio Branco (in Brazil) drain into the Amazon.
The ecoregion sits upon the Guiana Shield which underlies the northern region of South America. It consists of a rock basement with a variety of igneous and metamorphic rocks formed during different geological events.
The upland terraces and mountains of the Guiana Shield are remnants of highly weathered and ancient parent material consisting mostly of quartzitic or sandstone rocks, although granitic rock types persist in some areas. The lowland plains emerged only recently from lacustrine and marine environments. The soils are generally sandy and poor in nutrients.
The seasonal climate is humid to sub-humid with 2,000 to 2,400 mm (78 to 95 in) of rainfall distributed evenly though the year. The average annual temperature is approximately 24° C.
The region hosts 209 mammals. Many are widespread Amazonian species, including jaguars (Panthera onca), pumas (Puma concolor), tapirs (Tapirus terrestris), two peccaries (Tayassu pecari and T. tajacu), and deer (Mazama spp.). Other mammals that have a restricted distribution include several opossums (Didelphis albiventris, Lutreolina crassicaudata, and Marmosa robinsoni), bats (Pteronotus davyi, Lonchorhina fernandezi, and Sturnira ludovici), an endemic olingo (Bassaricyon beddardi), and endemic rodents (Sciurus flammifer, Proechimys hoplomyoides, and Dasyprocta guamara).
The avifauna is comprised of about 631 species, few of which are endemics. A number of species have a restricted distribution; however, including white-cheeked pintails (Anas bahamensis), aplomado falcons (Falco femoralis), brown-throated parakeets (Aratinga pertinax), pavonine cookoos (Dromococcyx pavoninus), vermiculated screech owls (Otus guatemalae), burrowing owls (Athene cunicularia), five species of emeralds and hummingbirds in the Amazilia genera, chestnut-tipped toucans (Aulacorhynchus derbianus), smoke-colored peewees (Contopus fumigatus), orange-crowned orioles (Icterus auricapillus), gray seedeaters (Sporophila intermedia), two-banded warblers (Basileuterus bivittatus), and black-backed water-tyrants (Fluvicola albiventer).
Reptiles and amphibians are abundant. The more famous snakes that occur here including the fer-de-lance (Bothrops asper), palm pit-vipers (Bothriechis spp.), coral snakes (Micrurus spp.), boa constrictors (Boa constrictor), and bushmasters (Lachesis muta). Iguanas (Iguana iguana) are ubiquitous and tegus lizards (Tupinambis) common.